On 09/15/2011 06:17 PM, Dave Hansen wrote: > On Thu, 2011-09-15 at 14:24 -0500, Seth Jennings wrote: >> How would you suggest that I measure xcfmalloc performance on a "very >> large set of workloads". I guess another form of that question is: How >> did xvmalloc do this? > > Well, it didn't have a competitor, so this probably wasn't done. :) > A lot of testing was done for xvmalloc (and its predecessor, tlsf) before it was integrated into zram: http://code.google.com/p/compcache/wiki/AllocatorsComparison http://code.google.com/p/compcache/wiki/xvMalloc http://code.google.com/p/compcache/wiki/xvMallocPerformance I think we can use the same set of testing tools. See: http://code.google.com/p/compcache/source/browse/#hg%2Fsub-projects%2Ftesting These tools do issue mix of alloc and frees each with some probability which can be adjusted in code. There is also a tool called "swap replay" which collects swap-out traces and simulates the same behavior in userspace, allowing allocator testing with "real world" traces. See: http://code.google.com/p/compcache/wiki/SwapReplay > I'd like to see a microbenchmarky sort of thing. Do a million (or 100 > million, whatever) allocations, and time it for both allocators doing > the same thing. You just need to do the *same* allocations for both. > > It'd be interesting to see the shape of a graph if you did: > > for (i = 0; i < BIG_NUMBER; i++) > for (j = MIN_ALLOC; j < MAX_ALLOC; j += BLOCK_SIZE) > alloc(j); > free(); > > ... basically for both allocators. Let's see how the graphs look. You > could do it a lot of different ways: alloc all, then free all, or alloc > one free one, etc... Maybe it will surprise us. Maybe the page > allocator overhead will dominate _everything_, and we won't even see the > x*malloc() functions show up. > > The other thing that's important is to think of cases like I described > that would cause either allocator to do extra splits/joins or be slow in > other ways. I expect xcfmalloc() to be slowest when it is allocating > and has to break down a reserve page. Let's say it does a bunch of ~3kb > allocations and has no pages on the freelists, it will: > > 1. scan each of the 64 freelists heads (512 bytes of cache) > 2. split a 4k page > 3. reinsert the 1k remainder > > Next time, it will: > > 1. scan, and find the 1k bit > 2. continue scanning, eventually touching each freelist... > 3. split a 4k page > 4. reinsert the 2k remainder > > It'll end up doing a scan/split/reinsert in 3/4 of the cases, I think. > The case of the freelists being quite empty will also be quite common > during times the pool is expanding. I think xvmalloc() will have some > of the same problems, but let's see if it does in practice. > Thanks, Nitin -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>